Orbital debris encompasses all non-functional human-made objects in Earth orbit, from entire defunct satellites and spent upper stages to paint flecks and fragments from collisions and explosions. The U.S. Space Surveillance Network tracks over 30,000 objects larger than 10 cm, but there are estimated to be millions of smaller fragments that cannot be tracked yet can still damage or destroy operational spacecraft at orbital velocities.
The debris problem is intensifying as the number of satellites in orbit grows exponentially. Notable debris-generating events include China's 2007 anti-satellite test and the 2009 Iridium-Cosmos collision. Active debris removal (ADR) is an emerging industry, with Astroscale, ClearSpace, and others developing vehicles to capture and deorbit large debris objects before they fragment into even more dangerous clouds.